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ST16C454 View Datasheet(PDF) - Exar Corporation

Part Name
Description
MFG CO.
'ST16C454' PDF : 29 Pages View PDF
ST16C454
Figure 8, Crystal oscillator connection
X1
1.8432 MHz
C1
C2
22pF
33pF
Loop-back Mode
The internal loop-back capability allows onboard diag-
nostics. In the loop-back mode the normal modem
interface pins are disconnected and reconfigured for
loop-back internally. MCR register bits 0-3 are used for
controlling loop-back diagnostic testing. In the loop-
back mode OP1 and OP2 in the MCR register (bits 3/
2) control the modem -RI and -CD inputs respectively.
MCR signals -DTR and -RTS (bits 0-1) are used to
control the modem -CTS and -DSR inputs respectively.
The transmitter output (TX) and the receiver input (RX)
are disconnected from their associated interface pins,
and instead are connected together internally (See
Figure 12). The -CTS, -DSR, -CD, and -RI are discon-
nected from their normal modem control inputs pins,
and instead are connected internally to -DTR, -RTS, -
OP1 and -OP2. Loop-back test data is entered into the
transmit holding register via the user data bus interface,
D0-D7. The transmit UART serializes the data and
passes the serial data to the receive UART via the
internal loop-back connection. The receive UART con-
verts the serial data back into parallel data that is then
made available at the user data interface, D0-D7. The
user optionally compares the received data to the initial
transmitted data for verifying error free operation of the
UART TX/RX circuits.
In this mode, the receiver and transmitter interrupts
are fully operational. The Modem Control Interrupts
are also operational. However, the interrupts can only
be read using lower four bits of the Modem Control
Register (MCR bits 0-3) instead of the four Modem
Status Register bits 4-7. The interrupts are still con-
trolled by the IER.
Rev. 3.31
12
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